1. Technical Field
The present invention relates to a three-phase electromagnetic motor in which a winding structure of magnetic poles formed between slots of a stator core is improved.
2. Description of Related Art
As an electromagnetic motor, a brushless motor or a Permanent Magnet Motor (PM type motor) is exemplified. When using a three-phase power supply in the electromagnetic motor, typically, windings of a u-phase, a v-phase, and a w-phase are disposed around magnetic poles of a stator core in this order so that the number of windings needs to be a multiple of three.
In order to minimize winding costs and connection costs in the three-phase electromagnetic motor, the minimum value of the number of windings is three. When winding in a concentrated manner with a number of windings of three is performed, two poles and three slots, and four poles and three slots are typical combinations of the number of poles and the number of slots. However, if the number of a permanent magnet poles is small, there is a problem that a cogging torque is increased.
In the related art, various techniques relating to a winding structure of an electromagnetic motor have been suggested. For example, a motor in which an auxiliary pole that is not subjected to winding is disposed between magnetic poles that are subjected to winding has been disclosed (see Japanese Unexamined Utility Model Registration Application Publication No. 59-90279). According to the technique of Japanese Unexamined Utility Model Registration Application Publication No. 59-90279, high efficiency of the motor is achieved by reducing manufacturing costs and increasing magnet utilization.
Furthermore, a motor is disclosed in which windings are disposed in every other magnetic pole and a width of a magnetic pole that is subjected to winding is greater than a width of a magnetic pole that is not subjected to winding (see Japanese Patent No. 4363132) . According to Japanese Patent No. 4363132, it is possible to improve the performance of insulation between windings of different phases adjacent to each other and it is possible to reduce winding costs.
Furthermore, a motor is disclosed in which a winding is continuously disposed in two poles and a magnetic pole that is not subjected to winding is disposed in a third magnetic pole (see Japanese Unexamined Patent Application Publication No 2004-304928). According to Japanese Unexamined Patent Application Publication No 2004-304928, it is possible to reduce winding costs and to achieve high efficiency for the motor.
However, the motor disclosed in Japanese Unexamined Utility Model Registration Application Publication No. 59-90279 is not suitable for a three-phase power supply because it has six poles and eight slots. The motor disclosed in Japanese Patent No. 4363132 has ten poles and twelve slots and the motor disclosed in Japanese Unexamined Patent Application Publication No. 2004-304928 has eight poles and nine slots and thereby is suitable for the three-phase power supply.
As described above, in the three-phase electromagnetic motor, when employing a combination of a typical number of poles and number of slots such as two poles and three slots or four poles and three slots, there is a problem that cogging torque is increased.
Therefore, in order to prevent an increase in cogging torque, a combination of eight poles and six slots, eight poles and nine slots, ten poles and twelve slots, or the like is often selected. That is, there is a contradictory relationship between cost reduction by reducing the number of windings and a reduction of the cogging torque.
However, a combination is conceivable in which the number of poles is much greater than the number of slots. For example, a combination of eight poles and three slots, ten poles and three slots, or the like may be considered. However, in this case, the cogging torque is reduced, but a short circuit of a magnet flux of a permanent magnet between poles occurs and motor efficiency is significantly reduced depending on the decrease in torque and thereby this configuration would almost certainly not be adopted.
Thus, development of a technique that can reduce winding costs and connecting costs, and achieve high efficiency for the motor by minimizing the number of windings (three windings) is required.